Light scattered from a molecule may be elastically scattered or inelastically scattered. Most of the photons are elastically scattered and have the same frequency and wavelength as the incident light. This elastic scattering is Rayleigh scattering. A small fraction of the light, approximately 1 in 10,000,000 photons, is inelastically scattered at frequencies usually lower than the frequency of the incident light. The frequency of the inelastically scattered light is dependent upon the molecules doing the scattering. This inelastic scattering is Raman scattering.
Generally, Rayleigh scattering is mediated by particles far smaller than the wavelength of the light. The particle sizes are approximately less than 40 nanometers (nm). However, another type of elastic scattering, Tyndall scattering, is mediated by much larger particles, particles approximately in the range from 40 nm to 900 nm. In Tyndall scattering, as in Rayleigh scattering, the intensity of the scattered light is dependent upon the fourth power of the frequency of the incident light. Therefore, blue light is scattered more strongly than red light. Tyndall scattering may be mediated by particles in a light-transmissive colloid or fine suspension.